The present invention relates to an aircraft cabin pressure control system for controlling aircraft cabin pressure during aircraft ascent, cruise and descent. In particular, a system is disclosed for adapting control of rates of cabin pressure changes to meet variable requirements of particular airlines, the airlines' specific route structures, and regional air traffic control standards.
Air pressure within an aircraft cabin is controlled during an entire flight profile to minimize passenger discomfort, and ensure a maximum pressure differential between the cabin and ambient pressures is not exceeded. In a typical flight from a coastal or sea-level city to a landing site slightly above sea level, at takeoff, pressure within the aircraft cabin (P.sub.c) and actual ambient pressure (P.sub.a) outside of the cabin are approximately the same, 14.70 pounds per square inch ("p.s.i."). The aircraft takes off and ascends to an altitude of 45,000 feet, for example, where P.sub.a decreases to approximately 2.14 p.s.i. Then, the aircraft cruises for a specific time at that altitude, until it descends to the landing site, which has an ambient pressure (P.sub.ld) slightly lower than the P.sub.a at take off. During such a flight, the cabin pressure decreases during the ascent so that a minimum human comfort pressure of approximately 10.92 p.s.i. (equivalent to an altitude of approximately 8,000 feet) is not exceeded, and the maximum differential between P.sub.a and P.sub.c is not exceeded, as well. During descent, P.sub.c increases so that it is approximately the same as the P.sub.ld slightly before the aircraft lands. That ensures P.sub.c is at a slightly higher pressure than P.sub.a when the aircraft lands, thereby allowing the aircraft doors to be opened easier in an emergency. Maximum passenger comfort during the flight is achieved by minimizing the rate of cabin pressure change during ascent and descent, so that the rates do not exceed the equivalent of approximately 500 feet per minute ("f.p.m.") for ascent and 300 f.p.m. for descent.
Known systems for controlling aircraft cabin pressure utilize a cockpit selector panel to communicate with an electronic cabin pressure controller, which actuates an outflow valve. The cabin is pressurized by compressed bleed air directed into the cabin from the aircraft's engines. Modulation by the controller of the outflow valve controls rate of air flow out of the cabin, thereby controlling cabin pressure.
As described in U.S. Pat. No. 3,473,460 to Emmons, incorporated herein by reference, and assigned to the assignee of the present invention, an automated system for controlling the rate of aircraft cabin pressure change is disclosed that utilizes the aforesaid three parameters, P.sub.a, P.sub.c and P.sub.ld, in a function generator (FIG. 1, No. 33) having a single, non-adjustable operating line as a function of the difference between P.sub.a and P.sub.ld to provide a set point for the desired rate of cabin pressure change. Such a non-adjustable operating line constrains control of cabin pressure rate changes to only values along the non-adjustable operating line of the function generator. Therefore, that system could not anticipate a literally infinite number of possible cabin pressure ascent and descent profiles resulting from geography, weather, air traffic control, etc.
An improved system for controlling the rates of aircraft cabin pressure change is disclosed in U.S. Pat. No. 5,186,681, filed on Sep. 30, 1991, incorporated herein by reference, and assigned to the assignee of the present invention. It discloses a method for generating a variable desired rate of cabin pressure change that utilizes schedules stored in the controller that incorporate specific rate limit set points, or that include non-linear functions correlating cabin pressure to ambient pressure or ambient pressure rates of change. The schedules are typically supplied by aircraft manufacturers, and attempt to typify a range of aircraft flight profiles.
Such schedules, however, have been unable to accommodate varying demands of a world-wide airline market. Typically, North American, European and Asian airlines utilize significantly different flight profiles. For example, an European airline having numerous flights between France and Italy would utilize much more rapid ascents and descents than an airline flying primarily up and down the East Coast of North America. Additionally, Asian operators frequently have unique cruise schedules, which impact rates of ascent and descent. Finally, regional air traffic control requirements (e.g., duration and frequency of holding patterns) likewise impact unique characteristics to an airline's typical flight profiles, rendering fixed, rate-limit or non-linear control schedules in need of custom adaptation for specific usage.
Accordingly, it is the general object of the present invention to provide an adaptive aircraft cabin pressure control system that overcomes the deficiencies of the prior art.
It is a more specific object to provide an adaptive aircraft cabin pressure control system that accommodates specific requirements of all airlines.
It is another specific object to provide an adaptive aircraft cabin pressure control system that can be implemented in existing aircraft cabin pressure control systems.
It is yet another object to provide an adaptive aircraft cabin pressure control system that automatically adapts existing schedules for controlling aircraft cabin pressure to requirements of a specific flight profile.
The above and other objects and advantages of this invention will become more readily apparent when the following description is read in conjunction with the accompanying drawings.